This invention relates generally to aircraft electric power generation systems, and more particularly, to such systems which include electromechanical components to perform a speed control function.
Aircraft electrical power generation systems which convert variable speed mechanical power produced by an aircraft engine into fixed frequency electrical power, fall into two basic categories. The first category includes constant speed drive generator systems in which a mechanical device is used to drive an electrical generator at a fixed speed, regardless of the speed of the prime mover. The constant speed generator, thus provides constant frequency power to the utilization loads.
The second category includes electronic power converters which are used to convert a generator's output to constant frequency electrical power. The generator can be connected directly to the engine, thus eliminating the mechanical constant speed drive. Such systems are referred to as variable speed constant frequency (VSCF) systems. Both types of systems are suitable for aircraft applications, however, each has advantages over the other.
Hydromechanical constant speed drives can cause severe transients and/or complete loss of power in zero gravity flight maneuvers. This is because the hydraulic system within the constant speed drive cannot properly sump the oil needed for the hydraulic drive motors. To overcome these deficiencies, the present invention combines features of systems in both categories in a unique manner to replace the hydraulic components in a constant speed drive system with electronic components to make an electromechanical constant speed drive.